U.S. patent number 5,545,164 [Application Number 08/241,768] was granted by the patent office on 1996-08-13 for occipital clamp assembly for cervical spine rod fixation.
This patent grant is currently assigned to Advanced Spine Fixation Systems, Incorporated. Invention is credited to Robert S. Howland.
United States Patent |
5,545,164 |
Howland |
August 13, 1996 |
Occipital clamp assembly for cervical spine rod fixation
Abstract
An occipital clamp assembly. The occipital clamp assembly
comprises a lower occipital plate for attachment to the skull of a
patient, wherein the lower occipital plate includes grooves in its
upper surface. An occipital plate stud mounted in the lower
occipital plate and upper occipital plates, having a groove in each
of their lower surfaces, mounted on the occipital plate stud
wherein the grooves of the lower occipital plate mate with the
grooves of the upper occipital plates to thereby form rod receiving
apertures. Also provided is means for securing the upper occipital
plate to the occipital plate stud and means for securing the lower
occipital plate to the skull.
Inventors: |
Howland; Robert S. (Seal Beach,
CA) |
Assignee: |
Advanced Spine Fixation Systems,
Incorporated (Cypress, CA)
|
Family
ID: |
22912101 |
Appl.
No.: |
08/241,768 |
Filed: |
May 12, 1994 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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998116 |
Dec 28, 1992 |
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Current U.S.
Class: |
606/250; 606/286;
606/71 |
Current CPC
Class: |
A61B
17/7041 (20130101); A61B 17/7055 (20130101); A61B
17/701 (20130101); A61B 17/7049 (20130101) |
Current International
Class: |
A61B
17/70 (20060101); A61B 017/70 () |
Field of
Search: |
;606/61,69,70,71,72,73,60,54,59 ;602/17,18,39 ;623/17 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Keith H. Birdwell, M.D., et al., "Texas Scottish Rite Hospital
(TSRH) Instrumentation System" The Textbook of Spinal Surgery, vol.
1, 1991, p. 221..
|
Primary Examiner: Tucker; Guy
Attorney, Agent or Firm: Christie, Parker & Hale,
LLP
Parent Case Text
RELATED APPLICATIONS
This application is a continuation in part of U.S. application Ser.
No. 07/998,116, filed Dec. 28, 1992, now abandoned, which is
incorporated herein by reference.
Claims
What is claimed is:
1. An occipital clamp assembly comprising:
a lower occipital plate having a plurality of apertures for
receiving means for directly securing the lower occipital plate to
the skull;
an upper occipital plate;
a plurality of plate studs for attaching the lower plate to the
upper plate;
means of securing the upper plate to the lower plate; and
a plurality of means for directly securing the lower occipital
plate to the skull wherein each one of the securing means is
located in each one of the lower occipital plate apertures;
wherein the lower occipital plate comprises:
a T-shaped plate wherein the plurality of apertures for receiving
means for directly securing the lower occipital plate to the skull
are located on the center bar of the T;
plate stud apertures at each end of the cross-bar of the T for
receiving the plate studs; and
grooves adjacent to each of the plate stud apertures for attachment
of rods.
2. An occipital clamp assembly as recited in claim 1 wherein the
plurality of means for directly securing the lower plate to the
skull comprises screws inserted through the lower occipital plate
apertures.
3. An occipital clamp assembly as recited in claim 1 wherein the
means of securing the plates comprises sleeve nuts, sleeve nuts are
substantially recessed into the upper occipital plates when
assembled on the occipital plate studs.
4. A cervical spine fixation system comprising:
cervical clamp assemblies each one comprising:
an bone screw for mounting in cervical vertebrae;
a clamping assembly mounted on the bone screw having a rod
receiving aperture, wherein the clamping assembly is dimensioned
for use in the cervical region of the spine;
means for attaching the clamping assembly to the bone screw;
an occipital plate assembly comprising:
a T-shaped lower occipital plate for direct attachment to the skull
of a patient, wherein the lower occipital plate includes grooves in
its upper surface at each end of the cross-bar of the T and a
plurality of apertures for receiving screws for directly securing
the lower occipital plate to the skull located in the center bar of
the T;
externally threaded occipital plate studs mounted in the T-shaped
lower occipital plate at each end of the cross-bar of the T;
upper occipital plates, having a groove in each one of the plates'
lower surface, mounted on the occipital plate studs wherein the
grooves of the lower occipital plate mate with the grooves of the
upper occipital plates to thereby form rod receiving apertures;
flat head screws for directly securing the lower occipital plate to
the skull, wherein the screws are located in the lower occipital
plate apertures; and
internally threaded nuts threaded onto the occipital plate studs
securing the upper occipital plate to the occipital plate stud;
and
spinal fixation rods, wherein the spinal fixation rods are secured
in the rod receiving apertures of the occipital plate assembly at a
first end and wherein the spinal fixation rods are secured in the
rod receiving apertures of the cervical clamp assemblies at a point
along their length.
Description
FIELD OF THE INVENTION
The present invention relates to instrumentation for fixation of
the cervical region of the spine and more particularly to
implantable fixation systems for attachment to the occipital region
of the skull.
BACKGROUND OF THE INVENTION
Every year there are a significant number of people who suffer
severe neck injuries from trauma. These injuries include cervical
fractures, fracture dislocations combined with retropulsion of the
disc and other major injuries. Also, each year many people undergo
cervical spine surgery for degenerative diseases, especially
degenerative spinal stenosis, which involves the removal of much of
the bone which supports the cervical region of the spine resulting
in instability of the cervical region.
Treatment of these conditions has included traction either with a
halter or with Crutchfield type tongs followed by application of a
cast or brace. If surgery is necessary, the area of injury is often
fixed with wire to allow fusion of the vertebrae in the affected
region of the vertebral column. Often the treatment includes
anterior decompression and fusion, or more recently, plates and
screws have been used to immobilize the unstable region. Such
plates may be used either anteriorly or posteriorly, or in a few
cases, both anteriorly and posteriorly.
While these fixation devices have been used effectively, they have
a number of serious disadvantages. For example, the use of wires
prevents flexion, as required for effective fixation, but does not
prevent rotation nor extension of the cervical region, which leads
to poor fixation of the vertebrae in this region. Currently, wires
are nearly always used in combination with bone grafts. Sometimes
the grafts are placed between the posterior elements of the
vertebrae in such a fashion as to prevent extension, and since the
wires prevent flexion, some stabilization is obtained. However, the
stabilization is usually insufficient to avoid the necessity for
the additional stability conferred by the use of halo devices,
large casts or braces.
In the case where posterior plates and lateral bone mass screws are
used, the stability is increased by simply screwing the plate into
the bone. However, since the bone in the cervical area is
relatively soft, the screws of such devices easily pull or cut out
of the bone and, therefore, do not immobilize well. Even if there
is no major failure of the device, such as the screws pulling out
of the bone, the screws eventually work loose and plates, that
initially prevented all motion, tend to loosen as the patient
recovers from the surgery and becomes more active. As a result,
halos, casts and braces are often used in conjunction with screw
and plate fixation.
Numerous fixation devices have been described, such as those
described in U.S. Pat. Nos. 5,030,220 and 5,034,011, for use in the
lumbar-sacrum regions of the spine. While these fixation devices
have proven successful for use in the lumbar region, the physiology
and structure of the cervical spine, C1 to C7, is very different
from the lumbar-sacrum regions. For example, the bone screws, when
placed in the lateral masses of the cervical vertebra, are usually
placed at an angle from horizontal, whereas in the lumbar region
they are placed in a horizontal plane. However, for proper
stabilization and fixation, the hardware carried by the bone screws
ought be such as to provide support and stabilization, generally
along the axis of the cervical portion of the spine, rather than at
an angle to it. It is desirable that a cervical fixation device be
developed which would preferably take into account these
considerations. In addition, it is desirable that a cervical
fixation device be relatively compact and easy to install.
SUMMARY OF THE INVENTION
The present invention relates to an occipital plate assembly. The
occipital plate assembly comprises a lower occipital plate for
attachment to the skull of a patient, wherein the lower occipital
plate includes grooves in its upper surface. An occipital plate
stud is mounted in the lower occipital plate and an upper occipital
plate is mounted on the occipital plate stud. The upper occipital
plate includes a groove in its lower surface. When the upper and
lower occipital plates are assembled together, the grooves of the
lower occipital plate mate with the grooves of the upper occipital
plate to form rod receiving apertures. Also provided is means for
securing the upper occipital plate to the occipital plate stud and
means for securing the lower occipital plate stud to the skull.
The occipital plate assembly is attached by the rod receiving
apertures to first ends of spinal fixation rods. The spinal
fixation rods are also clamped to cervical vertebrae to thereby
immobilize the cervical region of the spine.
DESCRIPTION OF THE DRAWINGS
Features, aspects and advantages of the present invention will be
more fully understood when considered with respect to the following
detailed description, appended claims and accompanying drawings
wherein:
FIG. 1 is a diagrammatic posterior view of the cervical spine;
FIG. 2 is a diagrammatic side view of the cervical spine
illustrating the cranial-ward orientation of the desired bone screw
locations;
FIG. 3 is a superior sectional diagrammatic view illustrating the
lateral orientation of the bone screw locations;
FIG. 4 is a perspective view illustrating the location of the bone
screws in accordance with this invention;
FIG. 5 is a perspective view illustrating the assembly of a rod on
a lower saddle in accordance with the present invention;
FIG. 6 is a view similar to FIG. 5 illustrating the completed
assembly in accordance with one embodiment of the present
invention;
FIG. 7 is a view similar to FIG. 5 illustrating the completed
assembly in accordance with a second embodiment of the present
invention;
FIG. 8 is a view similar to FIG. 5 illustrating the completed
assembly in accordance with a third embodiment of the present
invention;
FIG. 9 is a view, in section, of a bone screw taken along the line
9--9 of FIG. 10;
FIG. 10 is a side view of a bone screw in accordance with the
present invention;
FIG. 11 is a plan view of the bottom surface of the lower left hand
saddle;
FIG. 12 is a side view taken along the line 12--12 of FIG. 11;
FIG. 13 is a side view taken along the line 13--13 of FIG. 11;
FIG. 14 is an end view taken along the line 14--14 of FIG. 11;
FIGS. 15, 16, 17, and 18 are views similar to FIGS. 11, 12, 13 and
14 but illustrating a lower right hand saddle;
FIG. 19 is a plan view of the top surface of an upper left hand
saddle;
FIG. 20 is a side view taken along line 20--20 of FIG. 19;
FIG. 21 is a side view taken along line 21--21 of FIG. 19;
FIG. 22 is a side view taken along line 22--22 of FIG. 19, showing
the front face;
FIGS. 23, 24, and 25 are views similar to FIGS. 20, 21 and 22 but
illustrating an upper right hand saddle on which a lock washer is
secured;
FIG. 26 is a perspective view, as seen from the front face, on the
same side as the rod receiving aperture, illustrating the mating
fit of the upper and lower left saddles;
FIG. 27 is a plan view of a cervical screw spacer in accordance
with the present invention;
FIG. 28 is a side view of the spacer taken along line 28--28 of
FIG. 27;
FIGS. 29, 30, 31, and 32 are views similar to FIGS. 11, 12, 13, and
14 but illustrating a lower left hand saddle with an integral
spacer in accordance with the present invention;
FIG. 33 is a side view of another embodiment of an upper saddle for
use in the present invention;
FIG. 34 is a sleeve nut for use in clamping the upper saddle
illustrated in FIG. 33 to the bone screw;
FIG. 35 is a perspective view illustrating an occipital plate
assembly attached to the occipital squama, on either side of the
external occipital crest;
FIG. 36 is a plan view of a lower occipital plate;
FIG. 37 is a side view taken along line 38--38 of FIG. 36 of the
plate of FIG. 36 without an occipital plate stud assembled into the
lower occipital plate;
FIG. 38 is a side view taken along line 38--38 of FIG. 36 of the
plate of FIG. 36 with an occipital plate stud assembled into the
lower occipital plate;
FIG. 39 is a side view taken along line 39--39 of FIG. 36 of the
plate of FIG. 36 with an occipital plate stud assembled into the
lower occipital plate;
FIG. 40 is a plan view of the under side of an upper occipital
plate;
FIG. 41 is a side view of an upper and lower occipital plate
assembled together, taken along a line similar to that of 39--39 in
FIG. 36;
FIG. 42 is a plan view of an occipital plate stud;
FIG. 43 is a side view taken along line 43--43 of FIG. 42;
FIG. 44 is a top plan view of another embodiment of an occipital
plate which is shown partially assembled;
FIG. 45 is an exploded side view of the embodiment of FIG. 44;
FIG. 46 is a perspective view illustrating an occipital plate
assembly attached to the occipital crest with a cross-brace over
C1; and
FIG. 47 is a perspective view of a cross-brace.
DETAILED DESCRIPTION
The system of the present invention relates to a fixation system
which comprises bone screws, saddles, rods, clamps and nuts, all
uniquely structured for use in the cervical spine region. Fracture
dislocations and dislocations of the cervical spine are indications
in which the system of the present invention are likely to be of
most benefit. The screw and rod system of the present invention
would prevent virtually all motion in the spinal segments
instrumented. Two or more segments may be instrumented and
stabilized, if desired. If a patient has a severe fracture of the
lateral mass of a cervical vertebra, a broken segment may be
skipped, and three segments fused together. Cross-bracing may be
used over the skipped segment to prevent rotation in cases of
excessive instability. If there are multiple laminar fractures, the
system of the present invention may be used since there is no limit
to the number of levels which can be stabilized. Attachment to the
occipital bone at the skull may also be done safely and
efficiently.
If anterior decompression is necessary, due to retropulsed disc
material or bone, the system of the present invention may be
assembled posteriorly first, thus providing immediate fixation. The
surgeon may then proceed anteriorly, removing disc material and
grafting bone as necessary. In degenerative cervical disease, often
dramatic posterior decompression is necessary in order to
decompress the nerves adequately. The system of the present
invention may be used to stabilize the spine after these
procedures. In laminoplasty much of the external fixation with
casts or braces can be eliminated by use of the fixation system of
the present invention. Usually a light neck brace or soft collar is
sufficient.
In addition to the foregoing, the system of the present invention
may be used in the repair of a swan neck deformity. This deformity
results from extensive posterior decompression.
The system of the present invention, although intended for use
primarily in the cervical spine, may be extended into the upper
thoracic spine. For example, with pathology at C7 or T1, the screws
may be placed in the uppermost vertebrae of the thoracic spine and
also in the cervical spine, even though there is a rather marked
curvature in this area. The rods can be contoured to fit the
locations of the screws and saddles in any position or location.
The applications and principles of the present invention are
described in detail below.
FIG. 1 illustrates the cervical spine from C1 to C7. Labelled in
the drawing are the lateral mass 40, the superior facet 42, the
inferior facet 44 and the lamina 46. FIG. 2 illustrates the angle
between the outer surface 48 of the lateral mass and the transverse
left to right axis of the cervical spine, as indicated by the
dotted line 50. It is apparent that there is greater bone mass at a
cranial-ward angle than along the transverse axis 50. Thus, in
accordance with the present invention, the bone screws, described
in detail below, are installed in the lateral mass at a
cranial-ward angle of between 20.degree. and 30.degree., the angle
between the transverse axis 50 and line 52. In addition, in
accordance with the present invention the bone screws are also
angled lateral-ward between 10.degree. and 20.degree. as indicated
in FIG. 3, the angle between dotted line 54 (representing the
transverse axis front to back) and solid line 56.
FIGS. 4 to 8 illustrate the orientation and general sequence of
installing the fixation system of the present invention. As
illustrated in FIG. 4, bone screws 90, described in detail below,
are placed in the lateral mass, angled as described above. A spacer
270, described in detail below, has also been installed to raise
the bone screws to a desired elevation above the plane of the bone.
Bone screws are inserted on each side of the cervical spine.
Following insertion of the bone screws, a lower saddle 110 (a lower
left hand saddle) or 150 (a lower right hand saddle), which is
described in detail below, is assembled over the bone screw, as
shown in FIG. 5, and a rod 58 is placed in the lower saddle. If
desired a mastering procedure described in U.S. Pat. No. 4,653,481
may be used to configure the rod curvature.
The next step involves assembling an upper saddle 190 (an upper
left hand saddle) or 230 (an upper right hand saddle) over the bone
screw and rod, as shown in FIGS. 6 to 8. The entire assembly is
held together by a locking assembly 60 which operates to bolt the
upper and lower saddles onto the rod and to secure the saddles to
the bone screw. Each of the components of the fixation device are
described in detail below.
Referring to FIGS. 9 and 10, the details of the bone screw 90 are
illustrated. The bone screw and other components of the present
invention are preferably made of 316 LVM steel, although any other
appropriate material for surgical implantation, of equivalent
strength, may be used. In a preferred embodiment, the bone screw
includes a longitudinal axis and a first threaded end 92 for
screwing into the cervical vertebra. Adjacent to the first threaded
end is a flange section 94 and a clamp receiving section 96 is
adjacent to the flange. Located on an end remote from the threaded
end 90 is a second threaded end 98. The portion of the bone screw
from the flange 94 to the end of the threaded end 98 is generally
of a fixed dimension to accommodate the half-saddles and locking
mechanism. Typically this dimension is approximately 10 mm in
length, with a diameter of about 3.5 mm. The length of the bone
screw from the flange to the free end of the first threaded section
90 may vary from about 10 to 19 mm with a major thread diameter of
about 3.5 mm and a minor thread diameter of about 2.5 mm.
The flange diameter is about 5.3 mm and thus extends radially
beyond the outer diameter of the threaded end 92. A portion 100 of
the flange facing the first threaded section 90 is tapered, as
shown. The flange is oriented in a plane which is perpendicular to
the long axis of the bone screw. Located between the flange and the
threaded end 98 is a non-threaded cylindrical section 102 which has
a diameter greater than the diameter of the threaded section 98 but
smaller than the diameter of the flange. The cylindrical section
acts as a clamp receiving section for the upper and lower half
saddles. The clamp receiving section includes spaced exterior flat
sections 104 and 106 which mate with internal flat sections on the
lower saddle. These flat sections also permit the use of an
appropriate tool to thread the bone screw into the lateral mass of
the vertebrae.
FIGS. 11 to 14 illustrate a lower left hand saddle 110 which
includes an unthreaded aperture 112. The aperture has internal flat
sections 114 and 116 which mate with the flat sections 104 and 106
on the bone screw preventing rotation of the lower saddle relative
to the bone screw when the fixation system is assembled. The lower
saddle includes side faces 118 and 120, which are generally flat, a
curved rear face 122, a front face 124 and top and bottom faces 126
and 128, respectively.
Located in the top face 126 and between the aperture 112 and the
front face 124 is a groove, or rod receiving half aperture, 130 on
which a rod is received. The groove is preferably serrated, as
indicated at 132, the serrations extending axially from one side
face to the other to mate with serrations on the rod, which is
described in detail below.
The bottom face 128 of the lower saddle is generally flat and abuts
the flange 94 of the bone screw when assembled on the bone screw,
i.e., this face is oriented in a plane which is perpendicular to
the long axis of the bone screw. The top face 126 of the lower left
saddle is oriented in a plane which is at an angle to the bottom
face 128. Thus, the axial dimension of side face 118, of about 2.1
mm, is less than the axial dimension of side face 120, of about 4.8
mm, as measured along the long axis of the bone screw, the rear
face forming a gradual transition section whose axial dimension
progresses from that of side face 118 to that of side face 120.
Accordingly, the axial dimension from the bottom of the groove 130
to the bottom face along side face 118 is less than the axial
dimension from the bottom of the groove 130 to the bottom face
along side face 120.
This geometry places the groove at an inclined orientation which is
essentially parallel to the angular orientation of the top face of
the lower saddle, i.e., the plane of the groove is angularly
oriented with respect to the long axis of the bone screw. In order
to avoid sharp and bulky sections which may contact and damage the
bone of the vertebrae, a portion 134 of the bottom face 128
includes a taper which is narrow at the end adjacent to side face
118 and broader adjacent to side face 120 and forms a transition
section from the top face to the front face 124. As a result the
front face 124 is a relatively narrow section, see FIG. 14, which
is angularly oriented, represented by angle "a," in the same plane
as the top face. The angle "a" is between about 10.degree. to
25.degree., with 12.degree. or 22.degree. being preferred.
In FIGS. 15 to 18, a lower right hand saddle 150 is illustrated.
The lower right hand saddle is basically the same as the lower left
hand saddle already described, except that the angular orientation
is reversed. In these figures, the same numbers are used to
describe similar parts as described in FIGS. 11 to 14. In this form
face 118 has a greater axial length than face 120, while the top
face 126, as illustrated in FIG. 18, is oriented in an opposite
angular orientation as compared to face 126 of FIG. 14. Therefore,
left hand half-saddles are used for installation on the left hand
side of the vertebrae and right hand half-saddles are installed on
the right hand side of the vertebrae, thus allowing a common
angular displacement, cranial-ward, of the fixation device.
A upper left hand saddle 190, of one embodiment of the present
invention, is illustrated in FIGS. 19 to 22. The upper saddle
includes a bottom face 192 adapted to be positioned in facing
relation with the top face 126 of the lower saddle, side faces 194
and 196, a curved rear face 198 and a front face 200 and a top face
202. The upper saddle includes an unthreaded generally circular
aperture 204 which aligns with the aperture of the lower saddle and
when the assembly is place over the end 98 of the bone screw. There
are no interior flats in aperture 204.
Located in the bottom face 192 and between the aperture 204 and the
front face 200 is a groove, or rod receiving half aperture, 206 on
which a rod is received for clamping. The groove 206 is preferably
serrated, as indicated at 208, the serrations extending axially
from one side face to the other to mate with serrations on the rods
when the fixation device is assembled together.
The top face 202 of the upper saddle is generally flat and is
oriented in a plane which is perpendicular to the long axis of the
bone screw and generally parallel to the lower or bottom face 128
of the lower saddle. The bottom face 192 of the upper left saddle
is oriented in a plane angularly disposed with respect to the top
face 202, but in an angular orientation for a mating fit with the
face 126 of the lower saddle. Thus, the axial dimension of side
face 196, of about 2.1 mm, is less than the axial dimension of side
face 194, of about 4.8 mm, as measured along the long axis of the
bone screw, the rear face 198 again forming a gradual transition
section whose axial dimension progresses from that of side face 196
to that of side face 194. Accordingly, the axial dimension from the
bottom of the groove 206 to the top face along side face 196 is
less than the axial dimension from the bottom of the groove 206 to
the top face along side face 194.
This geometry, in effect, places the groove 206 in an inclined
orientation which is essentially parallel to the angular
orientation of the top face 126 of the upper saddle, i.e., the
plane of the groove is angularly oriented with respect to the long
axis of the bone screw. In order to avoid sharp and bulky sections
which may irritate the neck muscles of a patient when the fixation
device is installed, a portion 210 of the top face 202 includes a
taper which is narrow at the end adjacent side face 196 and broader
adjacent side face 194 and forms a transition section from the
bottom face 192 to the front face 200. In effect, the front face
200 is a relatively narrow section, see FIG. 22, which is angularly
oriented in the same plane as the top face at an angle "a". Angle
"a" is between about 10.degree. to 25.degree., with 12.degree. or
22.degree. being preferred.
The angular orientation of the rod receiving grooves with respect
to the long axis of the bone screws also results in a comparable
angular orientation of the rod with respect to the long axis of the
bone screws. Typically, the rods, made of the material already
described, are about 3.1 mm in diameter and may vary in length from
about 25 mm to at least about 100 mm as required for the fixation
procedure being performed. The outer surface of the rod is serrated
along its length, having for example 28 teeth and the serrations
match those on the grooves of the saddles.
Unlike the lower saddle, the upper saddle 190 in this embodiment of
the invention has provided in the top face 202 a blind aperture
212, the latter located between aperture 204 and the inclined
portion 210 of the top face. In one embodiment of the present
invention, described in detail below, a locking assembly 60
comprises a locking washer wherein a locking tang 220 of a lock
washer is received in this aperture 212. As illustrated on an upper
right hand saddle, in FIGS. 23 to 25, the lock washer 214 is a
separate item assembled between the upper saddle 230 and a nut 260,
see FIG. 7. The upper right hand saddle is basically the same as
the upper left hand saddle already described, except that the
angular orientation is reversed. In these figures, the same numbers
are used to describe similar parts as described in FIGS. 19 to
22.
In the assembly procedure one tang 220 of the washer is deformed
into the blind aperture, a nut 260 is threaded over the distal end
of the bone screw and tightened and the remaining tangs are
deformed to grip the sides of the nut, see FIG. 26. The lock washer
214 includes three tangs, 216 and 218 which are deformed upwardly,
and 220 which is deformed downwardly and received in the blind
aperture 212. Tang 220 effectively attaches the lock washer 214 to
the upper saddle. When tangs 216 and 218 are deformed upwardly they
lock the nut in place and prevent it from loosening after
installation.
In one embodiment of the present invention as seen in FIG. 26, once
the mating saddles, here the left hand saddles 150 and 190, are
mounted on the bone screw 90 and bolted together by the nut 260 and
lock washer 214 which, as mentioned, may be fixed to the upper
saddle, as shown in FIGS. 23 to 25, the assembly is essentially
completed. In the assembled form the tangs 216 and 218 are deformed
around a nut 260 threaded on the end 98 of the bone screw. Since
the lower saddle includes interior flats 116 and 114 which mate
with flats 106 and 104 on the bone screw, the lower saddle is
prevented from rotating relative to the bone screw. The upper
saddle is prevented from rotating relative to the lower saddle due
to the inclined mating faces 126 and 192. Moreover, since the
saddles, which form a rod clamp are bolted against the shoulder 94
of the bone screw, as contrasted to being bolted against the bone
of the cervical spine, there is substantial strength in the
completed assembly. Further, the rod(s) are firmly secured in the
clamp formed by the mating saddle assemblies which form a rod
receiving aperture since the grooves, or rod receiving half
apertures, and the rod are dimensioned for good purchase and
serrated to prevent rod rotation relative to the clamp. The above
is true of both the right and left hand configurations.
The lock nut illustrated FIG. 7 is a hexagonal nut, but other nuts
may be used. In a another embodiment of the present invention,
illustrated in FIG. 6, the locking nut is an acorn nut with a
smooth, curved top surface to reduce possible irritation to the
muscles which cover the fixation device when it is installed in a
patient.
Occasionally, it may be necessary to raise the saddle clamp
assembly above the level of the cervical bones to allow clearance
of the bone structure surrounding the saddle clamp assembly and to
reduce the amount of bending of the rod which connects to the
saddle clamps. One way of achieving this is by the use of a
cervical spacer 270 illustrated in FIGS. 27 and 28. The assembled
location of the spacer is shown in FIG. 4, between the tapered
under surface of the screw flange 94 and the cervical bone
structure. This spacer, made of material already described, is
generally cylindrical in shape and includes an aperture 272 through
which the bone screw passes. A counterbored section 274 mates with
the curved under surface 100 of the bone screw flange. Angularly
oriented face 276 normally rests against the bone, the angle "b"
being between 15.degree. and 35.degree.. The spacer provides
support for the portion of the bone screw which extends above the
bone and provides clearance, where desired.
A preferred embodiment of clamp assembly for providing a clearance
is illustrated in FIGS. 29 to 32 which illustrate a lower left hand
saddle assembly 290, which in all essential respects is the same as
the lower left hand saddle of FIGS. 11 to 14, save for the presence
of an integral spacer extension 292. As shown, the spacer 292 is
located on the bottom face 128 and includes a top surface 294 which
is essentially flat and planar and oriented in a plane which is
perpendicular to the long axis of the bone screw. In installation,
the top surface bears against the flange 94 of the bone screw, thus
raising the groove 130 a distance corresponding to the vertical
height 296 of the extension. The vertical height 296 may be varied
as needed. It is understood that a lower right hand saddle having
an integral spacer (not shown) could also be used.
In a preferred form, all parts thus far described are processed to
break all sharp edges and are electropolished and passivated. The
parts described may be sterilized prior to use by any of the known
sterilization procedures.
In use, the screws are located in the proper position, as
determined by the surgeon. The spacer may be placed on the bone
with the bone screw passing through the spacer. The lower saddle is
assembled over the bone screw. Several screws and saddle assemblies
may be installed. If the rod is to be configured, the mastering
technique referred to above may be used. The properly configured
final rod is then placed in the groove(s) and the upper saddle
assembly is placed over the lower saddle and secured in place by
any of the several devices already described.
In another embodiment of the present invention, illustrated in FIG.
8 the cervical fixation device is designed to minimize or reduce
irritation to the neck muscles which overlay the system once it has
been installed. In the system described above, the locking nut
extends beyond the clamping assembly. In some instances, the length
of the screw-clamp assembly tends to cause muscle irritation after
implantation. In this embodiment of the invention, a sleeve nut
fits into a recess on the upper surface of an upper half-clamp. The
novel sleeve nut in this embodiment of the present invention
greatly reduces the overall axial length of the screw-clamp
assembly, resulting in a low profile and smooth upper surface of
the fixation system which reduces the likelihood for the system's
causing the formation of a painful bursa. The upper and lower
saddle and bone screw are similar to those described above and will
only be described briefly here to point out the differences. The
same numbers are used for parts that are unchanged from the parts
described previously.
The lower saddles are essentially the same as described above and
illustrated in FIGS. 11 to 18.
An upper saddle 330 illustrated in FIG. 33, is provided with an
aperture 204 for receipt on the upper threaded end 98 of the bone
screw 90. The axial length of the upper-half clamp is greater than
that of the upper threaded end 98 of the bone screw so that, when
assembled, none of the threaded portion extends beyond the upper
saddle 330.
The internal diameter of the upper saddle aperture is stepped. A
lower section 332 has a diameter such that, when placed on the bone
screw, the upper saddle will fit securely against the cylindrical
section 102 of the bone screw. An intermediate section 334, which
abuts the lower section, has an intermediate diameter which is
greater than the diameter of the lower section. Adjacent the
intermediate section is an upper section 336, which has a diameter
larger than that of the intermediate section. The intermediate and
upper sections are separated by a chamfer line 338. When assembled,
the intermediate and upper sections accommodate a sleeve nut 340,
illustrated in FIG. 34 which is described in detail below.
The upper saddle also includes an arm 342 in which is a groove 130,
laterally of the aperture 204. The groove is serrated along its
length, as indicated at 132, for mating and gripping the serrated
rod. The geometry of the upper saddle is the same as described for
the upper half saddles described above and places the groove at an
inclined orientation which is essentially parallel to the angular
orientation of the top face of the lower saddle, i.e., the plane of
the groove is angularly oriented with respect to the long axis of
the bone screw. When assembled, the serrated surfaces of the upper
and lower saddles are in facing relation to each other and mate
with, and firmly grip, the serrated rod. When assembled, the lower
and upper saddles are placed on the bone screw, as described above.
A sleeve nut is used to hold the lower and upper saddles in place
on the bone screw flange 94 and to ensure a firm grip on the rod.
The sleeve nut is illustrated in FIG. 34. The sleeve nut 340 has an
aperture 344, which is threaded so that it mates with the threaded
portion 98 of the bone screw.
The exterior of the sleeve nut is of different diameters. At the
lower end of the sleeve nut, the diameter of the sleeve nut 346 is
at its smallest and is sized such that the sleeve nut will fit into
the stepped region 334 of the upper saddle. At the upper end of the
sleeve nut, and adjacent the small-diameter portion 346, is a
large-diameter portion of the sleeve nut 348. A fillet radius 350
is located at the juncture of the small- and large-diameter portion
of the sleeve nut. The large-diameter portion is sized so that it
will fit into the stepped region 336 of the upper saddle, thus
holding the upper saddle and the lower saddle securely in place
when the sleeve nut is screwed onto the bone screw. The stepped
interior of the upper saddle allows a distribution of the force
conferred by the sleeve nut on the upper saddle over a larger area.
A chamfer line 352 is locate at the bottom of the sleeve nut.
The top face 354 of the sleeve nut includes four radial notches
356, placed at equal distances from each other. The notches align
with prongs of a driver, not shown, so that the surgeon can more
easily attach the sleeve nut to the bone screw.
In use, the lower saddle is assembled over an bone screw, and then,
after the rod is in position, the upper half-clamp is installed.
The sleeve nut is then threaded on the upper threaded-end portion
of the bone screw and tightened down, using a driver. The prongs of
the driver are mated with the notches of the sleeve nut and the
driver is then used to tighten the sleeve nut into the upper
saddle. The sleeve nut, when tightened down, is completely
contained within the aperture 204, leaving exposed a small portion
of the upper edge of the face 358 of the upper saddle.
After the sleeve nut is in place, the exposed portion of the face
358 is crimped at one point along its periphery corresponding to
one of the radial notches. The crimp ensures that the sleeve nut is
firmly locked in place and that undesired rotation of the sleeve
nut is inhibited.
In the event that some adjustment, and hence removal of the sleeve
nut is necessary, the crimp is easily overcome by using the driver
to remove the sleeve nut, and the sleeve nut is unscrewed to
release the upper and lower saddles. After any required adjustment
has been made, the screw-and-clamp assembly is secured in place, as
described above.
The advantage of the low profile cervical fixation system of the
present invention is, that the axial length (height) of the
screw-clamp assembly is greatly reduced, when compared to the
height of other screw-clamp assemblies, since the axial length of
previous screws had to be of a dimension sufficient to accommodate
at least one nut and locking washer above the clamp. The height of
the screw-clamp assembly as installed increased the probability of
muscle irritation by the clamp assembly. Also, the installed
fixation system has a top surface which is in a single plane which
reduces muscle irritation. In one embodiment of the present
invention, the sleeve nut fits into a recess on the upper surface
of the upper saddle, greatly reducing the overall axial height of
the bone screw above the upper saddle. This low profile of the
fixation system reduces the likelihood of the system's causing the
formation of a painful bursa.
In another embodiment of the present invention the cervical
fixation system is used to treat damage to the spine in the region
of the first (atlas) or second (axis) cervical vertebra. In such
cases the fixation device is attached at one end to the cervical
vertebra, as described above. The other end is attached to the
occipital squama, on either side of the external occipital crest,
by an occipital plate assembly 350, as shown in FIG. 35. The
occipital plate assembly comprises a lower occipital plate 360
(illustrated in FIGS. 36 to 39 and 41), an upper occipital plate
400 (illustrated in FIGS. 40 and 41), an occipital plate stud 420
(illustrated in FIGS. 42 and 43), a nut 352, attached to the
occipital plate stud, and screws 354 attaching the lower occipital
plate to the occipital squama. A serrated rod 356 connects the
occipital plate assembly to the cervical assembly 358.
FIGS. 36 to 39 illustrate a lower occipital plate 360. The lower
occipital plate is a generally rectangular shaped plate 362 with an
outwardly extending arm 364 perpendicular to the rectangular shaped
plate, and located at the middle of one of the long sides of the
rectangle. The arm includes a groove 366 (see FIG. 39). The groove
is serrated along its length, as indicated at 368, for mating and
griping the serrated rod 356.
At either end of the rectangular shaped plate are apertures 370 for
receiving screws 354 and for attaching the occipital plate to the
occipital squama. Each aperture has a greater diameter 371 at an
upper side of the plate that the diameter 373 at a lower side of
the plate. The different diameters of the aperture allow the "V"
shaped head of the screw to seat into the aperture and to hold the
lower occipital plate onto the occipital squama.
Located between the apertures 370, adjacent to the arm, is a
generally cylindrical third aperture 372 (see FIG. 37). One
sidewall 374 of the aperture 372 is flattened (see FIG. 36). On an
under surface of the plate the aperture is counterbored 376. The
counterbored aperture 372 acts to seat a threaded occipital plate
stud 420. The stud has a flat section 430 on one side for mating
with the flattened sidewall of aperture 372. The flat sides act to
correctly locate the stud in aperture 372 and to prevent it
rotating relative to the lower occipital plate.
Located on the under side of the lower occipital plate are channels
378. The channels allow the lower occipital plate to flex so that
it can be molded to the gentle curve of the occipital squama and
thus lay flat against and conform to the occipital squama
surface.
Stud 420, illustrated in FIGS. 42 and 43, comprises a threaded end
422 which is adjacent to a non-threaded section of similar diameter
424. The non-threaded section abuts a shoulder 426 which separates
the non-threaded section 426 from a larger diameter second
non-threaded section 428. The diameter of the non-threaded section
428 is dimensioned so that it will fit "snugly" into aperture 370
when the plate stud is assembled into the lower occipital plate.
Non-threaded section 428 includes the flat section 430, described
above. Adjacent to non-threaded section 428 is a second shoulder
432 which has an increasing tapered diameter greater than that of
the non-threaded section 428 as it extends away from that section.
Shoulder 432 is of a larger diameter than the diameter of the
aperture 372. The counterbored section of the aperture 372 acts to
seat the shoulder 432. The larger diameter of shoulder 432 prevents
the stud from slipping through the aperture 372 when the stud and
lower occipital plate are assembled (see FIG. 38).
The upper occipital plate 400, illustrated in FIGS. 40 and 41, is a
rectangular shaped plate with an aperture 402 at one end of the
plate. The diameter of aperture 420 is dimensioned so that it will
fit "snugly" onto non-threaded section 424 when the upper occipital
plate is assembled onto the plate stud. Located at the other end of
the upper plate, on an under surface of the upper plate, is a
groove 404. When the upper plate is placed on the lower plate the
groove 404 aligns with the groove 368 of the lower plate to form a
rod receiving aperture for securely gripping the serrated rod
356.
In use, the occipital plate stud is slipped into the aperture 372
in the lower occipital plate so that it extends up away from the
occipital squama by aligning flat sections 430 and 374. The lower
occipital plate is then attached to the occipital squama using
screws 354. Once the lower plate is firmly attached to the
occipital squama, the upper plate is placed onto the stud and
aligned to bring the grooves 368 and 404 in facing relation to form
a rod receiving aperture. A rod is placed into the rod receiving
aperture and the upper plate is tightened to the lower plate.
In one embodiment of the present invention the upper plate is
clamped to the lower plate by screwing an acorn nut 352 onto the
threaded end of the stud. The acorn nut is locked into place with a
lock washer 353 which includes three deformable tangs 355 (only two
of which are shown in FIG. 35). Two of the tangs are deformed
upwardly, and one is deformed downwardly and received in the blind
aperture 406 (illustrated in FIG. 41). The downwardly deformed tang
effectively attaches the lock washer to the upper plate. The
upwardly deformed tangs lock the nut in place and prevent it from
loosening after installation. Such a nut and lock washer are
described above in relation to FIGS. 22 and 24 to 26, and are
identical to the nut and lock washer for attachment of the upper
plate.
In an alternate embodiment, the locking assembly comprises a low
profile system which includes a locking nut which fits into a
recess on the upper surface of the upper plate. Such a low profile
system is described in conjunction with FIGS. 33 and 34, and a
similar system can be used for attachment of the upper plate. In
the case of a low profile system, the upper plate is modified to
include the stepped sections (as illustrated in FIG. 33) into the
upper surface of the upper occipital plate, around aperture 402.
The upper plate is then attached to the plate stud with a nut
similar to that illustrated in FIG. 34.
In another embodiment of the present invention, illustrated in
FIGS. 44 to 46, the occipital plate assembly is designed for
attachment to the occipital crest. The occipital plate assembly 440
comprises an occipital plate 442, rod clamps 444, occipital plate
studs 446 (similar to element 420 described above), nuts 448 for
attaching the clamp to the occipital plate stud, and screws 450 for
attaching the occipital plate to the occipital crest. A serrated
rod 356 connects the occipital plate assembly to cervical clamp
assemblies 358 (see FIG. 46). This assembly has the advantage of
being attached to the occipital crest which has thicker bone than
other parts of the skull.
FIGS. 44 and 45 illustrate an occipital plate assembly 440. A lower
occipital plate is a generally "T" shaped flat plate 442. Located
at either end of the cross-bar of the "T" are upwardly facing
grooves 452. The grooves are serrated along their length, as
indicated at 454, for mating and griping the serrated rods 356 (see
FIG. 46). Adjacent to the grooves are apertures 458 which are
generally cylindrical. One sidewall 460 of the aperture 458 is
flattened (see FIG. 44). On an under surface of the plate the
aperture is counterbored 462 (see FIG. 45). The counterbored
aperture acts to seat a threaded occipital plate stud 446 (see FIG.
45). The stud 446 is the same as stud 420, illustrated in FIGS. 42
and 43, and the same reference numerals are used for the same
parts. The stud has a flat section 430 on one side for mating with
the flattened sidewall of the aperture. The flat sides act to
correctly locate the stud in the aperture and to prevent it from
rotating relative to the lower occipital plate once installed.
Along the upright of the "T" are apertures 510 for receiving screws
450 (see FIG. 46) and for attaching the occipital plate to the
occipital crest. Each aperture has a greater diameter 512 at an
upper side of the plate than the diameter 514 at a lower side of
the plate. The different diameters of the aperture allow the head
of the screw to seat into the aperture and to hold the lower
occipital plate onto the occipital crest.
Located on the under side of the lower occipital plate are channels
464. The channels allow the occipital plate to flex so that it can
be molded to the gentle curve of the occipital region of the skull
and thus lay flat against and conform to the skull surface.
The clamps or upper occipital plates 444 are similar to clamps 400
illustrated in FIGS. 40 and 41. The same reference numerals are
used for similar parts. The clamps are rectangular shaped with an
aperture 402 adjacent to a groove 404. The groove includes
serrations which are shown at 470. In one embodiment of the present
invention the aperture 402 includes stepped sections 466 and 468.
The lower section 468 of the aperture is dimensioned so that it
will fit the lower section 346 of a sleeve nut such as 448 (which
is the same as sleeve nut 340 described in FIG. 34 above and the
same reference numerals are used for the same parts). The upper
section 466 is dimensioned to accommodate the upper section of
sleeve nut 448. The internal aperture 344 of the sleeve nut is
threaded and dimensioned to fit onto stud 446. When the clamp is
placed on the occipital plate, groove 452 aligns with the groove
404 of the clamp to form a rod receiving aperture for securely
gripping the serrated rod 356.
In use, occipital plate studs are slipped into apertures 458 in the
occipital plate so that they extend up and away from the lower
surface of the occipital plate. The flat sections of the aperture
and the stud are aligned to prevent rotation of the studs relative
to the occipital plate. The occipital plate is then attached to the
skull using screws 450. Once the occipital plate is firmly attached
to the skull, clamps 444 are placed onto the stud and aligned to
bring the grooves 404 and 452 in facing relation to form rod
receiving apertures. Rods are placed into the rod receiving
apertures and the clamps are tightened to the occipital plate by
tightening sleeve nuts 448 onto studs 446. After the sleeve nuts
are in place, an exposed portion of the clamp is crimped as
described above. The crimp ensures that the sleeve nuts are firmly
locked in place and that undesired rotation of the sleeve nuts is
inhibited.
In some cases it is desirable to include cross-bracing to prevent
rotation in cases of excessive instability. FIG. 47 illustrates a
cross-brace 480. The cross-brace comprises a threaded rod 482.
Attached to a first end of the threaded rod is a fixed clamp 484.
At a second end of the threaded rod is an adjustable clamp 486.
The fixed clamp comprises two half clamps, 488 and 490, lock washer
492 (which is similar to lock washers 353 and 214 illustrated in
FIGS. 35 and 26, respectively) and nut 494 (which is similar to nut
260 illustrated in FIG. 26). The half-clamps 488 and 490 each
include an aperture 496 for threading onto the threaded rod and a
groove 498 adjacent to the aperture.
The adjustable clamp comprises two half clamps, 500 and 502 (which
are similar to half-clamp 490), two lock washers 492 and two nuts
494. The half-clamps 500 and 502 also each include an aperture 496
for threading onto the threaded rod and a groove 498 adjacent to
the aperture.
In use nut 494, lock washer 492 and half-clamp 490 are threaded, in
order, onto a first end of the threaded rod. The half-clamp 490 is
oriented such that the groove is facing toward the first end of the
threaded rod. Half-clamp 488 is then attached to the end of the
threaded rod by electron beam welding or other suitable means of
attachment. The half-clamp 488 is oriented such that the groove is
facing away from the first end of the threaded rod and toward the
groove of half-clamp 490 such that the grooves can align to form a
rod receiving aperture.
Nut 494, lock washer 492, half-clamp 500, half-clamp 502, a second
lock washer 492 and a second nut 494 are threaded, in order, onto
the second end of the threaded rod. The half-clamp 500 is oriented
such that the groove is facing toward the second end of the
threaded rod. The half-clamp 502 is oriented such that the groove
is facing away from the second end of the threaded rod and toward
the groove of half-clamp 502 such that the grooves can align to
form a rod receiving aperture.
The rod receiving aperture of clamp 484 is placed over a serrated
rod on one side of the vertebrae (see FIG. 46) and nut 496 is
tightened to clamp half-clamp 490 onto the rod and against
half-clamp 488 thus securing the clamp to the rod. Tangs of the
lock washer are then bent into a hole on the surface of the
half-clamp 490 (not shown) and up around the nut, as described
above, to prevent nut 494 from rotating and coming loose after
installation.
The groove of half-clamp 500 is placed against a serrated rod on
the side of the vertebrae opposite that of clamp 484 (see FIG. 46)
and one nut 494 is tightened to clamp half-clamp 490 onto the rod.
The groove of half-clamp 502 is placed against on the other side of
the serrated rod, opposite half-clamp 500 and the second nut 494 is
tightened to clamp half-clamp 502 onto the rod, thus securing the
clamp to the rod. Tangs of the lock washers are then bent into a
hole on the surface of the half-clamp 500 and 502 (not shown) and
up around the nut, as described above, to prevent nut 494 from
rotating and coming loose after installation.
This cross-brace allows for adjustable installation to cross-brace
rods which are at different distances, but, since one of the
half-clamps is fixed on the rod, the amount of manual manipulation
required to achieve the required adjustment is minimized.
It is apparent from the foregoing detailed description that the
present invention has many advantages over the support systems and
methods of the prior art as applied to the cervical spine. It will
be apparent that various modifications may be made to the support
system and methodology of the present invention by those skilled in
the art without departing from the scope of the appended
claims.
* * * * *